text: /* 
   * User address space access functions.
   *
   * Copyright 1997 Andi Kleen <ak@muc.de>
   * Copyright 1997 Linus Torvalds
   * Copyright 2002 Andi Kleen <ak@suse.de>
   */
  #include <linux/module.h>
  #include <asm/uaccess.h>
  
  /*
   * Copy a null terminated string from userspace.
   */
  
  #define __do_strncpy_from_user(dst,src,count,res)			   \
  do {									   \
  	long __d0, __d1, __d2;						   \
  	might_fault();							   \
  	__asm__ __volatile__(						   \
  		"	testq %1,%1\n"					   \
  		"	jz 2f\n"					   \
  		"0:	lodsb\n"					   \
  		"	stosb\n"					   \
  		"	testb %%al,%%al\n"				   \
  		"	jz 1f\n"					   \
  		"	decq %1\n"					   \
  		"	jnz 0b\n"					   \
  		"1:	subq %1,%0\n"					   \
  		"2:\n"							   \
  		".section .fixup,\"ax\"\n"				   \
  		"3:	movq %5,%0\n"					   \
  		"	jmp 2b\n"					   \
  		".previous\n"						   \
  		_ASM_EXTABLE(0b,3b)					   \
  		: "=&r"(res), "=&c"(count), "=&a" (__d0), "=&S" (__d1),	   \
  		  "=&D" (__d2)						   \
  		: "i"(-EFAULT), "0"(count), "1"(count), "3"(src), "4"(dst) \
  		: "memory");						   \
  } while (0)
  
  long
  __strncpy_from_user(char *dst, const char __user *src, long count)
  {
  	long res;
  	__do_strncpy_from_user(dst, src, count, res);
  	return res;
  }
  EXPORT_SYMBOL(__strncpy_from_user);
  
  long
  strncpy_from_user(char *dst, const char __user *src, long count)
  {
  	long res = -EFAULT;
  	if (access_ok(VERIFY_READ, src, 1))
  		return __strncpy_from_user(dst, src, count);
  	return res;
  }
  EXPORT_SYMBOL(strncpy_from_user);
  
  /*
   * Zero Userspace
   */
  
  unsigned long __clear_user(void __user *addr, unsigned long size)
  {
  	long __d0;
  	might_fault();
  	/* no memory constraint because it doesn't change any memory gcc knows
  	   about */
  	asm volatile(
  		"	testq  %[size8],%[size8]\n"
  		"	jz     4f\n"
  		"0:	movq %[zero],(%[dst])\n"
  		"	addq   %[eight],%[dst]\n"
  		"	decl %%ecx ; jnz   0b\n"
  		"4:	movq  %[size1],%%rcx\n"
  		"	testl %%ecx,%%ecx\n"
  		"	jz     2f\n"
  		"1:	movb   %b[zero],(%[dst])\n"
  		"	incq   %[dst]\n"
  		"	decl %%ecx ; jnz  1b\n"
  		"2:\n"
  		".section .fixup,\"ax\"\n"
  		"3:	lea 0(%[size1],%[size8],8),%[size8]\n"
  		"	jmp 2b\n"
  		".previous\n"
  		_ASM_EXTABLE(0b,3b)
  		_ASM_EXTABLE(1b,2b)
  		: [size8] "=&c"(size), [dst] "=&D" (__d0)
  		: [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr),
  		  [zero] "r" (0UL), [eight] "r" (8UL));
  	return size;
  }
  EXPORT_SYMBOL(__clear_user);
  
  unsigned long clear_user(void __user *to, unsigned long n)
  {
  	if (access_ok(VERIFY_WRITE, to, n))
  		return __clear_user(to, n);
  	return n;
  }
  EXPORT_SYMBOL(clear_user);
  
  /*
   * Return the size of a string (including the ending 0)
   *
   * Return 0 on exception, a value greater than N if too long
   */
  
  long __strnlen_user(const char __user *s, long n)
  {
  	long res = 0;
  	char c;
  
  	while (1) {
  		if (res>n)
  			return n+1;
  		if (__get_user(c, s))
  			return 0;
  		if (!c)
  			return res+1;
  		res++;
  		s++;
  	}
  }
  EXPORT_SYMBOL(__strnlen_user);
  
  long strnlen_user(const char __user *s, long n)
  {
  	if (!access_ok(VERIFY_READ, s, 1))
  		return 0;
  	return __strnlen_user(s, n);
  }
  EXPORT_SYMBOL(strnlen_user);
  
  long strlen_user(const char __user *s)
  {
  	long res = 0;
  	char c;
  
  	for (;;) {
  		if (get_user(c, s))
  			return 0;
  		if (!c)
  			return res+1;
  		res++;
  		s++;
  	}
  }
  EXPORT_SYMBOL(strlen_user);
  
  unsigned long copy_in_user(void __user *to, const void __user *from, unsigned len)
  {
  	if (access_ok(VERIFY_WRITE, to, len) && access_ok(VERIFY_READ, from, len)) { 
  		return copy_user_generic((__force void *)to, (__force void *)from, len);
  	} 
  	return len;		
  }
  EXPORT_SYMBOL(copy_in_user);
  
  /*
   * Try to copy last bytes and clear the rest if needed.
   * Since protection fault in copy_from/to_user is not a normal situation,
   * it is not necessary to optimize tail handling.
   */
  unsigned long
  copy_user_handle_tail(char *to, char *from, unsigned len, unsigned zerorest)
  {
  	char c;
  	unsigned zero_len;
  
  	for (; len; --len) {
  		if (__get_user_nocheck(c, from++, sizeof(char)))
  			break;
  		if (__put_user_nocheck(c, to++, sizeof(char)))
  			break;
  	}
  
  	for (c = 0, zero_len = len; zerorest && zero_len; --zero_len)
  		if (__put_user_nocheck(c, to++, sizeof(char)))
  			break;
  	return len;
  }
  